Taking high-precision Metrohm ion chromatography to an even higher level of autonomy, the Process IC can connect up to 20 sample streams and provide reliable multicomponent results for superior process control.

Problems with Dilution Titration (suppressor determination)

Conditioning is taking a long time and a standard deviation < 0.5% cannot be achieved.

B. The baseline has not been set correctly. The baseline needs to be defined identically for each addition.

The evaluation criterion has been reached. However, no results are being displayed.

In exceptional cases, the evaluation algorithm cannot calculate results with the "Nonlinear regression technique" curve type. You should be able to solve the problem by selecting the "Linear Interpolation" curve type.

The curve obtained from the sample looks different to that from the calibration.

This effect is not uncommon. It is caused by degradation products in the bath sample. With successful determination of recovery in a "check standard", the method can be checked at any time.

Problems with MLAT/LAT (brightener determination)

The reproducibility of results is worse than expected.

A. The electrodes were lifted out of the measuring solution when the sample was added. Please use the pipette opening for sample addition.

During the measurement, the temperature of the measuring solution should be kept constant. If a warm or hot bath sample is transferred into the measuring vessel, then the temperature should be adjusted. If necessary, it is possible to work with a measuring vessel with thermostat jacket (see image) and an external thermostat/cryostat. For more information, download our technical poster.

The measuring signal for the VMS is fluctuating.

The room temperature and/or the solution temperature are not constant: The room and solution temperature should be kept stable during the measurements (± 4 °C).

The reference potential is drifting away: Maintenance of the reference electrode should be carried out in accordance with the electrode leaflet.

The measuring vessel and the electrodes have been contaminated with organic additives. Thoroughly rinse the measuring vessel and the electrodes and use fresh VMS.

The signal is not decreasing despite suppressor addition.

No chloride is contained in the VMS: Check the preparation of the VMS and modify if necessary.

The electrode test is failing.

One or more electrodes are not connected: Check the electrode cable connections.

One or more electrodes are defective: Carry out maintenance according to the electrode data sheet. The measuring vessel does not contain enough solution or is empty: Check the fill level of the measuring vessel and add solution if required.

The peak is no longer recognized.

The reference potential is offset: Perform maintenance for the reference electrode in accordance with the electrode data sheet.

Conditioning is taking a long time.

The reference electrode is not yet equilibrated: After maintenance of the reference electrode, wait for at least 20 min before starting a measurement.

The platinum electrode tip is contaminated: Condition the working electrode in pure VMS.

The platinum electrode tip has been used for a very long time: Immerse the platinum electrode tip in c(NaOH) = 0.5 mol/L for approx. 10 min and then thoroughly rinse with distilled water. Replace the platinum electrode tip if necessary.

The VMS is contaminated: Check whether the reagents are clean. Only reagents with degree of purity "analytical grade" or better should be used.

The water quality is poor: Use distilled water, type-II grade (ASTM D1193-91) or higher.

The measuring solution is contaminated by diffusion: No infeed tubing other than the four-way micro dosing tip (6.1824.000) may be immersed in the measuring solution.

The measurement curves are noisy.

Contact problem at the driving axle (6.1204.x10 or 6.1204.x20): Remove any abrasion residue from the driving axle. If necessary, replace the driving axle.

Is it possible to repair a defective driving axle (6.1204.x010 or 6.1204.x20)?

It is not possible to repair the driving axle. The driving axle is a consumable and needs to be replaced at regular intervals. Driving axles with a mercury contact are supplied in a bag under protective nitrogen atmosphere. We recommend keeping the storage time of driving axles with a mercury contact as short as possible.

The measured values are widely scattered.

The solutions used are pipetted manually: The solution can be added with 800 Dosinos with dosing units to obtain reproducible results.

The solutions are not added through the pipette opening: During a measurement the solutions should only be added through the pipette opening.

Problems with the hardware

An electrode connector on the electrode cable is broken.

The electrode cable has accidentally been jammed in the measuring head cover or a cable contact has been bent: On the 894 Professional CVS you can replace the electrode cable set (see 894 Professional CVS manual). On the 797 VA Computrace this needs to be handled by Metrohm Service.

Solution is leaking between the 894 Professional CVS and the measuring head.

The measuring head is not correctly locked in place on the measuring head arm: Allow the measuring head to snap into place; you need to hear it click.

The membrane pumps of the 843 Pump Station are not operating at full pump capacity.

The cables are not connected or not connected correctly:

Connect the cables in accordance with the instructions in the manual.

The tubing connections are leaking:

Check the tubing connections and tighten, if necessary.

The rinse and/or waste canister are sealed air-tight:

Loosen the caps on the canisters a little or remove them.

The peristaltic pump on the sample changer is not transferring the entire sample to the measuring vessel.

The contact pressure of the tubing cartridge is set too low: Set the contact pressure of the tubing cartridge in accordance with the sample changer manual.

The pump time of the peristaltic pump is increasing: The pump tubing of the peristaltic pump has aged or is defective and should be replaced.

The PEEK sample needle on the Sample Processor is positioned more than 0.5 mm from the bottom of the sample vial: Position the PEEK sample needle in accordance with the information in the manual.

General problems

How often should the dosing units be prepared?

The dosing units used must be prepared at least once a day before measuring begins. This ensures that fresh solution is used for the analysis.

Preparing the Dosinos is taking a long time. Is it possible to speed up this step?

Port 3 of the dosing unit used can be connected to a waste canister using an outlet tubing. The outlet (port) 3 can be defined for the waste in the software (General settings or Configuration). With these settings, a significantly quicker preparation is ensured.

What preparatory steps need to be taken before shutting down the measuring system?

All dosing units used should be rinsed with distilled water in order to prevent a possible crystallization of metal salts.

At what intervals should a dosing unit be cleaned?

The dosing units used should be disassembled and thoroughly cleaned at 14-day intervals.

How should the electrodes be stored?

Auxiliary, reference, and working electrodes should be stored in distilled water. Storage in VMS is not recommended. If the measuring system is not used for an extended period (>24 h), then the reference electrode should be stored separately in c(KCl) = 3 mol/L. The other electrodes can also be stored dry.

How frequently do the electrodes need to be conditioned?

It is advisable to condition the electrodes at least once a day before you start work.

The measuring signal in VMS is exceptionally small and conditioning in VMS is taking a long time. What is the reason for that?

Most likely, the VMS in the measuring vessel is contaminated. The contamination might have been caused by the chemicals used but also by organic additives.

The measurement curves are noisy. What is the reason for that?

The driving axle is defective and needs to be replaced.

Can measurements made using other software be used in viva?

No, this is not possible.

How should the additives be stored?

The solutions should be protected from direct sunlight. If possible, the solutions should be stored in glass vessels. Unless specified otherwise, additives should be stored at room temperature.

Rotating disk electrode

Can platinum electrode tips be polished?

Metrohm does not recommend any mechanical treatment of platinum RDEs, e.g., by polishing with aluminum oxide!

Can Metrohm polish platinum electrode tips?

For logistical and technical reasons, Metrohm cannot offer a polishing service for used platinum electrode tips.

How do I clean my platinum electrode tip?

A contaminated platinum electrode tip can be conditioned in VMS or diluted H2SO4.

To clean a contaminated platinum electrode tip, it can be stored for approx. 60 minutes in c(NaOH) = 1 mol/L. Afterwards, the electrode should be well rinsed with isopropanol and deionized water.

The platinum electrode tip may not be treated in an ultrasonic bath.

The electrode surface of the platinum electrode tip is coated with a foreign metal (Cu, Sn, etc.). What can I do?

The platinum electrode tip can be immersed for a few seconds in concentrated nitric acid to oxidize a metal coating which has accidentally been applied. If after another measurement foreign metal should be found on the surface again, then the method parameters and electrode connectors need to be checked.

How temperature-resistant is the platinum electrode tip?

Platinum electrode tips with a glass shaft can be operated up to a maximum temperature of 50 °C.

Platinum electrode tips with a PEEK shaft can be operated up to a maximum temperature of 40 °C.

Can the platinum electrode tip be treated in an ultrasonic bath?

No, the platinum electrode tip may not be treated in an ultrasonic bath. This will irreversibly damage the electrode.

Does the Pt RDE diameter affect my analysis results?

The potentiostat integrated in the Metrohm CVS instruments can easily measure the smallest current with a high degree of precision. For this reason, it is also possible to get precise measurement results with smaller platinum electrode tip diameters. In a few exceptional cases, the method parameters need to be adjusted.

Reference electrode

My reference electrode has dried out. Can I regenerate it again?

Here you will learn what is to be done if the reference electrode ever dries out.

The 6.0728.x40 reference system cannot be regenerated if it dries out. The electrode must be replaced.

Dried-out KCl gel cannot be removed from the electrolyte vessel. The electrolyte vessel must be replaced.

Once the gel filling of the electrode 6.0730.x00 has dried up, the gel reference electrode is irrevocably damaged and must be replaced!

Until now, I have always used diluted H2SO4 as a bridge electrolyte. Can I use another electrolyte instead of KNO3?

The electrolyte vessel can be filled with any electrolyte that is a good conductor. If KNO3 interferes with the determination, you can use diluted H2SO4, for example, instead of c(KNO3). However, you should not change the electrolyte in the internal reference system. If another electrolyte is used here instead of c(KCl) = 3 mol/L, then the reference potential changes. This is also the case if you are using a different concentration of KCl.

How often do I need to change the reference electrolyte?

A correct reference potential of the reference electrode is an important factor for perfect results in CVS analysis. We recommended that you change the reference electrolyte c(KCl) = 3 mol/L at least every three days.

How often does the bridge electrolyte need changing?

The bridge electrolyte forms an electrical bridge between the measuring solution and the reference electrode. In many cases a strongly acidic measuring solution is used in CVS analysis. Over time, the acid may also reach the bridge electrolyte and thereby change the reference potential. This is why changing the bridge electrolyte every day is recommended.

The reference electrodes filled with KCl gel are maintenance-free, which means that no electrolyte needs to/may be changed.

Auxiliary electrode

The electrode surface of the auxiliary electrode is coated with a foreign metal (Cu, Sn, etc.). What can I do?

The auxiliary electrode can be immersed for a few seconds in concentrated nitric acid to oxidize an accidentally applied metal coating. If after another measurement foreign metal should be found on the surface again, then the method parameters and electrode connectors need to be checked.

Is polishing the platinum pin of the auxiliary electrode allowed?

As a general rule, the auxiliary electrode is maintenance-free and does not require any special cleaning. If you want to mechanically clean the platinum pin, then you can also polish the surface. Make sure that you do not rotate the platinum pin while doing so because otherwise the internal contact may break.